We often encounter datasets that include weak experimental phases that we must depend on in order to solve our structures. The following two datasets are examples of data collected for the purposes of solving structures by Single-wavelength Anomalous Diffraction (SAD) phasing. The anomalous signal is present, but weak, and therefore care must be taken to preserve the anomalous signal for phasing. This demonstration will educate the user on how to preserve the anomalous differences in a dataset.

SSRL data

Initial run

ALS data

We've already noticed that the beam centre recorded in the header needs to be converted in order to match the actual image. So we could tell autoPROC about that by using

% process BeamCentreFrom="header:x,-y" -d 01 | tee 01.lis

However, we also noticed that the diffraction seems to get weaker towards the end of data collection. So lets switch on a series of options that try and take care of such potential issues (apart from beam centre convention and loss of diffraction power, it also tries and deals with ice-rings):

% process -M automatic -d 01 | tee 01.lis

This reads a so-called macro (named "automatic") - for a list of macros please run process -M list.

Notes

The POINTLESS step in determining the most likely spacegroup comes up with P4212 (ALS infl) and P41212 (ALS hrem and SSRL data). Although there is still some checking to be done, it seems most likely that we have P41212 (or the enantiomorph P43212).